This application claims the priority of German patent document 101 34 345.0, filed Jul. 14, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a system for functional testing in a continuous-wave radar.
Continuous wave radars, primarily frequency modulated (FMCW), are used for measuring distances or for imaging the environment. For testing the functional capability of the radar system, it is desirable to feed a high-frequency test signal as closely as possible to the radar antenna, and to compare the output signal of the overall system with a defined pattern. In a basic form, this is approximated in the case of altimeters (aviation) by connecting a delay line into the antenna feeding line, so that an individual target of a known distance (that is, the line length of the delay line) can be measured in the altimeter radar system. In other applications, such delay lines are undesirable for weight and space reasons, and a separate sinusoidal high-frequency signal is generated in the frequency generating module, which high-frequency signal is fed into the antenna or into the high-frequency module. Considerable expenditures are required in each case because the corresponding measures concern components and modules in the high-frequency part.
The invention is based on a continuous-wave radar of the type that contains a transmitter circuit for generating radar transmit signals, a transmit/receive antenna coupled to the transmitter circuit via a circulator, and a receiver circuit coupled by way of the circulator by means of its input with the transmit/receive antenna, for processing radar echo signals of a target object received at the transmit/receive antenna. The circulator relays the transmit signals generated by the transmitter circuit to the transmit/receive antenna, and splits off the echo signals of the target object received from the transmit/receive antenna to the input of the receiver circuit. An RPC (Reflected Power Canceller) circuit coupled between the output and the input of the receiver circuit suppresses portions of the transmit signals that are split off from the transmitter circuit and/or reflected from the transmit/receive antenna directly (that is, not as an echo signal) into the receiver circuit. The latter contains a modulator connected into the signal path of the transmit signal, for generating a correction signal compensating the directly branched-off portions of the transmit signals. Such continuous-wave radars are known from German Patent Documents DE 199 18 767 A1 and DE 101 34 386.8, from European Patent Document EP 0 364 036 A2 or from European Patent Document EP 0 372 641 A2.
The RPC circuit that suppresses the portion of the transmit signal branched off without radiation and back-reception by way of the transmit-receive antenna directly into the receiver circuit of the radar is described in the references indicated for this purpose in German Patent Document DE 199 18 767 A1.
Generally, known RPC circuits provide a control loop in which the portions of the transmit signal approaching the input of the receiver circuit and split-off directly from the transmitter circuit or reflected by reflection from the transmit/receive antenna are superimposed with an additional signal split-off from the transmitter and being of opposite phase thereto, such that a complete deletion is achieved. In this manner, a disadvantageous coupling-over of transmitter noise and a reflection from the antenna to the receiver circuit are suppressed.
The radars may be pure continuous-wave radars with a fixed frequency without modulation, or Doppler radars as well as frequency-modulated (FMCW) pulsed or interrupted CW radars.
One object of the invention is to provide a system for functional testing in a continuous-wave radar which can be implemented in a simple manner and without high additional circuit-related expenditures. In particular, the additional components required for the functional testing should result in no large weight or space requirement.
This and other objects and advantages are achieved by the system for the functional testing in a continuous-wave radar according to the invention, which system contains a transmitter circuit for generating radar transmit signals, a transmit/receive antenna coupled by way of a circulator with the transmitter circuit, and a receiver circuit whose input is coupled with the transmit/receive antenna by way of the circulator, for processing radar echo signals of a target object received at the transmit/receive antenna. The circulator relays the transmit signals generated by the transmitter circuit to the transmit/receive antenna, and splits off the echo signals of the target object received from the transmit/receive antenna, and feeds them to the input of the receiver circuit. An RPC circuit coupled between the output and the input of the receiver circuit suppresses portions of the transmit signals that are split off from the transmitter circuit and/or reflected from the transmit/receive antenna directly into the receiver circuit. The RPC circuit contains a modulator that generates a correction signal, which compensates the directly split off portions of the transmit signals. According to the invention, the modulator generates a test signal equal to a radar echo signal suitable for the functional testing in response to a control signal fed from the outside.
An important advantage of the system according to the invention is the fact that it utilizes the already existing modulator of the RPC circuit for generating a high-frequency test signal for the functional testing of the continuous-wave radar. As a result, only a small number of additional components is required for implementing the system for the functional testing. A special advantage is the fact that no additional expenditures are required in the area of the high-frequency module but only in the area of the baseband electronic system which can be implemented at low cost. Nevertheless, the system according to the invention permits the testing of the function of the entire high-frequency part, except for the transmit/receive antenna.
A function generator for generating the control signal fed to the modulator from the outside is preferably coupled with the modulator of the RPC circuit.
The modulator preferably has control inputs for receiving in-phase and phase quadrature components of a baseband signal for the receiver circuit, and the function generator generates in-phase and phase quadrature components of a baseband test signal as the control signal at the inputs of the modulator.
Advantageously, an adder circuit provided at the input of the modulator combines the control signal generated by the function generator with a feedback signal returned from the receiver circuit to the modulator for the purpose of suppressing the transmit signals branched off directly into the receiver circuit.
The adder circuit preferably contains one adder respectively coupled with the inputs of the modulator, for combining the in-phase and quadrature components of the baseband test signal generated by the function generator as the control signal for the modulator with the in-phase and quadrature components of the baseband signal of the receiver circuit.
According to an advantageous alternative embodiment of the invention, it is provided that the modulator of the RPC circuit, for coupling the correction signal compensating the directly branched off portions of the transmit signal and/or the test signal generated in response to the control signal fed from the outside, is provided in the signal path between the circulator and the input of the receiver circuit.
According to an alternative advantageous embodiment of the invention, the modulator of the RPC circuit (for coupling the correction signal compensating the directly branched-off portions of the transmit signal and/or the test signal generated in response to the control signal fed from the outside) is provided in the signal path between the circulator and the transmit/receive antenna and is coupled by way of the circulator with the input of the receiver circuit.
According to an advantageous embodiment of the invention, the function generator contains a programmable signal processor and a digital-to-analog converter connected to the signal processor, for generating the control signal fed to the modulator from the outside.
According to another advantageous embodiment, the function generator contains a memory with a fixedly stored data set and a digital-to-analog converter connected thereto for generating the control signal fed from the outside to the modulator.
According to an embodiment of the invention, the function generator generates a sinusoidal control signal.
According to another, particularly advantageous embodiment of the invention, the function generator generates one or more complex control signals which can be superimposed.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.